Methods for producing synthesis gas by partial oxidation are well known in practice.
Generally, a (hydro)carbonaceous stream such as coal, brown coal, peat, wood, coke, soot, or other gaseous, liquid or solid fuel or mixture thereof, is partially combusted in a gasification reactor (or otherwise partially oxidised) using an oxygen containing gas such as substantially pure oxygen or (optionally oxygen-enriched) air or the like, thereby obtaining a product stream containing a.o. synthesis gas (i.e. CO and H2) and CO2.
The product stream is usually further processed, e.g. to cool the product stream in a quench section and to remove undesired components. Also, the product stream may be subjected to shift conversion, wet gas scrubbing and the like, depending on the end use of the product stream or parts thereof.
In the known method of producing synthesis gas, the quality of the product stream obtained may vary, due to e.g. disturbances or variations in the carbonaceous stream and the oxygen containing stream being fed to the gasification reactor, the amount of ash in the carbonaceous stream, etc. If for example coal is used as the carbonaceous stream, variations in H2O content of the coal may result in altered process conditions in the gasification reactor, as a result of which the composition of the product stream will also vary. Various methods of controlling a partial oxidation process are known. For example GB-A-837074 describes a process wherein the carbon dioxide in the product gas of a partial oxidation process is measured to control the steam flow.
U.S. Pat. No. 2,941,877 describes a process for controlling the oxygen-to-carbon feed ratio in a partial oxidation reactor. The oxygen-to-carbon feed ratio is controlled by measuring the methane concentration in the product gas using infrared measurement technique. A disadvantage of using methane as the control input is that the signal is not a sharp signal, making control less accurate.
The quality variation mentioned above may be even more pertinent if the end user of (parts of) the product stream desires a constant quality with only very limited variations therein.